U.S. patent application number 13/129358 was filed with the patent office on 2011-10-13 for organic semiconductors.
This patent application is currently assigned to Cambridge Display Tecnology Limited. Invention is credited to Sheena Zuberi, Tania Zuberi.
Application Number | 20110250719 13/129358 |
Document ID | / |
Family ID | 40230940 |
Filed Date | 2011-10-13 |
United States Patent
Application |
20110250719 |
Kind Code |
A1 |
Zuberi; Tania ; et
al. |
October 13, 2011 |
Organic Semiconductors
Abstract
An organic semiconducting compound comprising the structure of
formula (I): ##STR00001## where Ar.sub.1, Ar.sub.2, Ar.sub.3 and
Ar.sub.4 independently comprise monocyclic aromatic rings and at
least one of Ar.sub.1, Ar.sub.2, Ar.sub.3 and Ar.sub.4 is
substituted with at least one substituent X, which in each
occurrence may be the same or different and is selected from the
group consisting of (i) optionally substituted straight, branched
or cyclic alkyl chains with 1 to 20 carbon atoms, alkoxy, amino,
amido, silyl or alkenyl, or (ii) a polymerisable or reactive group
selected from the group consisting of halogens, boronic acids,
diboronic acids and esters of boronic acids and diboronic acids,
alkylene groups and stannyl groups, and where Ar.sub.1, Ar.sub.2,
Ar.sub.3 and Ar.sub.4 may each optionally be fused to one or more
further rings. The organic semiconducting compound is used as an
active layer in an organic semiconducting device such as a thin
film transistor.
Inventors: |
Zuberi; Tania; (Middlesex,
GB) ; Zuberi; Sheena; (Middlesex, GB) |
Assignee: |
Cambridge Display Tecnology
Limited
Cambridgeshire
GB
|
Family ID: |
40230940 |
Appl. No.: |
13/129358 |
Filed: |
November 27, 2009 |
PCT Filed: |
November 27, 2009 |
PCT NO: |
PCT/GB2009/002735 |
371 Date: |
June 21, 2011 |
Current U.S.
Class: |
438/99 ; 252/500;
257/E51.027; 549/41 |
Current CPC
Class: |
C09K 2211/1416 20130101;
C09K 2211/1092 20130101; H01L 51/0545 20130101; C09K 2211/1011
20130101; C09K 2211/1458 20130101; H05B 33/10 20130101; C09K 11/06
20130101; H01L 51/0074 20130101; C07D 495/22 20130101; C09K
2211/1425 20130101 |
Class at
Publication: |
438/99 ; 549/41;
252/500; 257/E51.027 |
International
Class: |
H01L 51/30 20060101
H01L051/30; H01B 1/12 20060101 H01B001/12; C07D 333/50 20060101
C07D333/50 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2008 |
GB |
0821703.6 |
Claims
1. An organic semiconducting device comprising an organic
semiconducting compound of formula (I): ##STR00019## where
Ar.sub.1, Ar.sub.2, Ar.sub.3 and Ar.sub.4 independently comprise
monocyclic aromatic rings and at least one of Ar.sub.1, Ar.sub.2,
Ar.sub.3 and Ar.sub.4 is substituted with at least one substituent
X, which in each occurrence may be the same or different and is
selected from the group consisting of (i) optionally substituted
straight, branched or cyclic alkyl chains with 1 to 20 carbon
atoms, alkoxy, amino, amido, silyl or alkenyl, or (ii) a
polymerizable or reactive group selected from the group consisting
of halogens, boronic acids, diboronic acids and esters of boronic
acids and diboronic acids, alkylene groups and stannyl groups, and
where Ar.sub.1, Ar.sub.2, Ar.sub.3 and Ar.sub.4 may each optionally
be fused to one or more further rings, and wherein at least one of
Ar.sub.1, Ar.sub.2, Ar.sub.3 and Ar.sub.4 comprises a heterocyclic
aromatic group.
2. A device according to claim 1 wherein a further aryl group
Ar.sub.5 is fused with Ar.sub.3 to provide a structure of formula
(II): ##STR00020## wherein Ar.sub.5 represents a monocyclic
aromatic ring optionally substituted with one or more substituents
X.
3. A device according to claim 2 wherein the aryl group Ar.sub.5
comprises a heterocyclic aromatic group.
4. A device according to claim 2 wherein Ar.sub.4 is fused to a
further aryl system Ar.sub.6 to provide a structure of formula
(III): ##STR00021## wherein Ar.sub.6 represents a monocyclic
aromatic ring optionally substituted with one or more substituents
X.
5. A device according to claim 4 wherein aryl system Ar.sub.6
comprises a heterocyclic aromatic group.
6. A device according to claim 4 wherein Ar.sub.5 is fused to a
further aryl system Ar.sub.7 to provide a structure of formula
(IV): ##STR00022## wherein Ar.sub.7 represents a monocyclic
aromatic ring optionally substituted with one or more substituents
X.
7. A device according to claim 6 wherein aryl system Ar.sub.7
comprises a heterocyclic aromatic group.
8. A device according to claim 1 wherein the semiconducting
compound comprises the structure: ##STR00023## where X.sub.1 and
X.sub.2 may be the same or different and are selected from
substituents X.; Z.sub.1 and Z.sub.2 are independently S, O, Se or
NR.sub.1, and where W.sub.1 and W.sub.2 are independently S, O, Se,
NR.sub.1 or --CR.sub.1.dbd.CR.sub.1--, where R.sub.1 is H or a
substituent group.
9. A device according to claim 1 wherein the semiconducting
compound comprises the structure: ##STR00024## where V.sub.1 and
V.sub.2 are independently S, O, Se or NR.sub.1, and where W.sub.1
and W.sub.2 are independently S, O, Se, NR.sub.1 or
--CR.sub.1.dbd.CR.sub.1--, where R.sub.1 is H or a substituent
group.
10. A device according to claim 1 wherein the semiconducting
compound comprises the structure: ##STR00025##
11. A semiconducting compound according to claim 1 wherein the
semiconducting compound comprises the structure: ##STR00026##
wherein X.sub.1--X.sub.10, which may be the same or different, are
selected from substituents X.
12. A device according to claim 1, wherein the compound comprises
an oligomer or polymer.
13. A thin film transistor comprising a device according to claim
1.
14. An optical device comprising a thin film transistor according
to claim 13.
15. An electroluminescent device comprising a thin film transistor
according to claim 13.
16. A solution for forming a thin film transistor, the solution
comprising a solute comprising an organic semiconducting compound
of formula (I): ##STR00027## where Ar.sub.1, Ar.sub.2, Ar.sub.3 and
Ar.sub.4 independently comprise monocyclic aromatic rings and at
least one of Ar.sub.1, Ar.sub.2, Ar.sub.3 and Ar.sub.4 is
substituted with at least one substituent X, which in each
occurrence may be the same or different and is selected from the
group consisting of (i) optionally substituted straight, branched
or cyclic alkyl chains with 1 to 20 carbon atoms, alkoxy, amino,
amido, silyl'or alkenyl, or (ii) a polymerizable or reactive group
selected from the group consisting of halogens, boronic acids,
diboronic acids and esters of boronic acids and diboronic acids,
alkylene groups and stannyl groups, and where Ar.sub.1, Ar.sub.2,
Ar.sub.3 and Ar.sub.4 may each optionally be fused to one or more
further rings, and wherein at least one of Ar.sub.1, Ar.sub.2,
Ar.sub.3 and Ar.sub.4 comprises a heterocyclic aromatic group.
17. A solution according to claim 16 comprising a solvent selected
from the group consisting of substituted benzenes.
18. A method for forming, a transistor comprising applying a
solution according to claim 16 to a substrate.
19. A method according to claim 18 comprising applying the solution
by ink-jet printing.
20. A method for synthesizing a semiconductive compound, the method
comprising fusing one or more further aryl groups to a compound
comprising the structure: ##STR00028## where Z.sub.1 and Z.sub.2
are independently S, O, Se, NR, or NCH, where R.sub.1 is H or a
substituent group, and X.sub.1 and X.sub.2 which may be the same or
different, are selected from substituents X; and wherein the one or
more of the further aryl groups may be heterocyclic.
21. A method according to claim 20 comprising synthesizing the
fused compound by a Suzuki coupling reaction.
22. A semiconductive compound comprising a structure selected from
the group consisting of: ##STR00029## ##STR00030## ##STR00031##
23. An organic semiconducting compound comprising a single bond or
divalent linker group linking two units of formula (I):
##STR00032## wherein Ar.sub.1, Ar.sub.2, Ar.sub.3 and Ar.sub.4 are
as defined in claim 1 and each unit of formula (I) is the same or
different.
24. A solution according to claim 17 comprising a solvent selected
from the group consisting of benzenes substituted with one or more
substituents selected from halogen and alkyl.
Description
[0001] The present invention relates generally to organic
semiconductor materials and in particular to organic semiconductors
for forming part of a thin film transistor.
BACKGROUND OF THE INVENTION
[0002] Transistors can be divided into two main types: bipolar
junction transistors and field-effect transistors. Both types share
a common structure comprising three electrodes with a
semiconductive material disposed there between in a channel region.
The three electrodes of a bipolar junction transistor are known as
the emitter, collector and base, whereas in a field-effect
transistor the three electrodes are known as the source, drain and
gate. Bipolar junction transistors may be described as
current-operated devices as the current between the emitter and
collector is controlled by the current flowing between the base and
emitter. In contrast, field-effect transistors may be described as
voltage-operated devices as the current flowing between source and
drain is controlled by the voltage between the gate and the
source.
[0003] Transistors can also be classified as p-type and n-type
according to whether they comprise semiconductive material which
conducts positive charge carriers (holes) or negative charge
carriers (electrons) respectively. The semiconductive material may
be selected according to its ability to accept, conduct, and donate
charge. The ability of the semiconductive material to accept,
conduct and donate holes or electrons can be enhanced by doping the
material.
[0004] For example, a p-type transistor device can be formed by
selecting a semiconductive material which is efficient at
accepting, conducting, and donating holes, and selecting a material
for the source and drain electrodes which is efficient at injecting
and accepting holes from the semiconductive material. Good
energy-level matching of the Fermi-level in the electrodes with the
HOMO level of the semiconductive material can enhance hole
injection and acceptance. In contrast, an n-type transistor device
can be formed by selecting a semiconductive material which is
efficient at accepting, conducting, and donating electrons, and
selecting a material for the source and drain electrodes which is
efficient at injecting electrons into, and accepting electrons
from, the semiconductive material. Good energy-level matching of
the Fermi-level in the electrodes with the LUMO level of the
semiconductive material can enhance electron injection and
acceptance.
[0005] Transistors can be formed by depositing the components in
thin films to form a thin film transistor (TFT). When an organic
material is used as the semiconductive material in such a device,
it is known as an organic thin film transistor (OTFT).
[0006] OTFTs may be manufactured by low cost, low temperature
methods such as solution processing. Moreover, OTFTs are compatible
with flexible plastic substrates, offering the prospect of
large-scale manufacture of OTFTs on flexible substrates in a
roll-to-roll process.
[0007] With reference to FIG. 4, the general architecture of a
bottom-gate organic thin film transistor (OTFT) comprises a gate
electrode 12 deposited on a substrate 10. An insulating layer 11 of
dielectric material is deposited over the gate electrode 12 and
source and drain electrodes 13, 14 are deposited over the
insulating layer 11 of dielectric material. The source and drain
electrodes 13, 14 are spaced apart to define a channel region
therebetween located over the gate electrode 12. An organic
semiconductor (OSC) material 15 is deposited in the channel region
for connecting the source and drain electrodes 13, 14. The OSC
material 15 may extend at least partially over the source and drain
electrodes 13, 14.
[0008] Alternatively, it is known to provide a gate electrode at
the top of an organic thin film transistor to form a so-called
top-gate organic thin film transistor. In such an architecture,
source and drain electrodes are deposited on a substrate and spaced
apart to define a channel region there between. A layer of an
organic semiconductor material is deposited in the channel region
to connect the source and drain electrodes and may extend at least
partially over the source and drain electrodes. An insulating layer
of dielectric material is deposited over the organic semiconductor
material and may also extend at least partially over the source and
drain electrodes. A gate electrode is deposited over the insulating
layer and located over the channel region.
[0009] An organic thin film transistor can be fabricated on a rigid
or flexible substrate. Rigid substrates may be selected from glass
or silicon and flexible substrates may comprise thin glass or
plastics such as poly(ethylene-terephthalate) (PET),
poly(ethylene-naphthalate) (PEN), polycarbonate and polyimide.
[0010] The organic semiconductive material may be made solution
processable through the use of a suitable solvent. Exemplary
solvents include mono- or poly-alkylbenzenes such as toluene and
xylene; tetralin; and chloroform. Preferred solution deposition
techniques include spin coating and ink jet printing. Other
solution deposition techniques include dip-coating, roll printing
and screen printing.
[0011] The length of the channel defined between the source and
drain electrodes may be up to 500 microns, but preferably the
length is less than 200 microns, more preferably less than 100
microns, most preferably less than 20 microns.
[0012] The gate electrode can be selected from a wide range of
conducting materials for example a metal (e.g. gold) or metal
compound (e.g. indium tin oxide). Alternatively, conductive
polymers may be deposited as the gate electrode. Such conductive
polymers may be deposited from solution using, for example, spin
coating or ink jet printing techniques and other solution
deposition techniques discussed above.
[0013] The insulating layer comprises a dielectric material
selected from insulating materials having a high resistivity. The
dielectric constant, k, of the dielectric is typically around 2-3
although materials with a high value of k are desirable because the
capacitance that is achievable for an OTFT is directly proportional
to k, and the drain current ID is directly proportional to the
capacitance. Thus, in order to achieve high drain currents with low
operational voltages, OTFTs with thin dielectric layers in the
channel region are preferred.
[0014] The dielectric material may be organic or inorganic.
Preferred inorganic materials include SiO.sub.2, SiN.sub.x and
spin-on-glass (SOG). Preferred organic materials are generally
polymers and include insulating polymers such as poly vinylalcohol
(PVA), polyvinylpyrrolidine (PVP), acrylates such as
polymethylmethacrylate (PMMA), fluorinated polymers and
benzocyclobutanes (BCBs) available from Dow Corning. The insulating
layer may be formed from a blend of materials or comprise a
multi-layered structure.
[0015] The dielectric material may be deposited by thermal
evaporation, vacuum processing or lamination techniques as are
known in the art. Alternatively, the dielectric material may be
deposited from solution using, for example, spin coating or ink jet
printing techniques and other solution deposition techniques
discussed above.
[0016] If the dielectric material is deposited from solution onto
the organic semiconductor, it should not result in dissolution of
the organic semiconductor. Likewise, the dielectric material should
not be dissolved if the organic semiconductor is deposited onto it
from solution. Techniques to avoid such dissolution include: use of
orthogonal solvents for example use of a solvent for deposition of
the uppermost layer that does not dissolve the underlying layer;
and cross linking of the underlying layer.
[0017] The thickness of the insulating layer is preferably less
than 2 micrometres, more preferably less than 500 nm.
[0018] Organic semiconductors are a class of organic molecules
having extensively conjugated pi systems allowing for the movement
of electrons.
[0019] Preferred methods for preparation of these molecules are
Suzuki reactions (coupling or polymerisation reactions) as
described in, for example, WO 2000/53656 and Yamamoto
polymerisation as described in, for example, T. Yamamoto,
"Electrically Conducting And Thermally Stable pi-Conjugated
Poly(arylene)s Prepared by Organometallic Processes", Progress in
Polymer Science 1993, 17, 1153-1205. These techniques both operate
via a "metal insertion" wherein the metal atom of a metal complex
catalyst is inserted between an aryl group and a leaving group of a
monomer. In the case of Yamamoto polymerisation, a nickel complex
catalyst is used; in the case of Suzuki reaction, a palladium
complex catalyst is used.
[0020] For example, in the synthesis of a linear polymer by
Yamamoto polymerisation, a monomer having two reactive halogen
groups is used. Similarly, according to the method of Suzuki
reaction, at least one reactive group is a boron derivative group
such as a boronic acid or boronic ester and the other reactive
group is a halogen. Preferred halogens are chlorine, bromine and
iodine, most preferably bromine.
[0021] Alternatively, stannyl groups may be used as reactive groups
in polymerisation or coupling reactions (Stille reactions).
[0022] The performance of organic semiconductors is typically
assessed by measurement of its "charge mobility" (cm.sup.2 V.sup.-1
s.sup.-1), which may relate to either the mobility of holes or
electrons. This measurement relates to the drift velocity of charge
carriers to an applied electric field across a material.
[0023] Organic semiconductors having relatively high mobilities
tend to be those which comprise compounds having a rigid planar
structure with extensive conjugation which allows for efficient and
effective pi-pi stacking in the solid state.
[0024] WO 2007/068618 describes a variety of organic
semiconductors, each comprising an array of fused aromatic rings
having a central benzene ring substituted with acetylene
groups.
[0025] JP 2007/088222 and WO 2007/116660 describe the use of
benzodithiophenes and its derivatives in small molecule, oligomeric
and polymeric form, as organic semiconductors.
[0026] However, the increased level of conjugation required to
allow compounds to form such a pi-pi stack may also result in a
decrease in band gap and stability of the semiconductor, leading to
poor performance and a short lifetime. Moreover, these compounds
may be highly insoluble due to the size of molecule required to
achieve extended conjugation, which poses particular problems in
synthesis and renders their use in efficient transistor production
methods, such as ink-jet printing, difficult.
SUMMARY OF THE INVENTION
[0027] The present invention seeks to provide an organic
semiconductor having high mobility, good solubility and good
stability (in particular stability in the ambient environment such
as stability to oxidation).
[0028] In a first aspect, the present invention relates to an
organic semiconducting device comprising an organic semiconducting
compound of formula (I):
##STR00002##
[0029] where Ar.sub.1, Ar.sub.2, Ar.sub.3 and Ar.sub.4
independently comprise monocyclic aromatic rings and at least one
of Ar.sub.1, Ar.sub.2, Ar.sub.3 and Ar.sub.4 is substituted with at
least one substituent X, which in each occurrence may be the same
or different and is selected from the group consisting of (i)
optionally substituted straight, branched or cyclic alkyl chains
with 1 to 20 carbon atoms, alkoxy, amino, amido, silyl or alkenyl,
or (ii) a polymerisable or reactive group selected from the group
consisting of halogens, boronic acids, diboronic acids and esters
of boronic acids and diboronic acids, alkylene groups and stannyl
groups, and where Ar.sub.1, Ar.sub.2, Ar.sub.3 and Ar.sub.4 may
each optionally be fused to one or more further rings.
[0030] The groups Ar.sub.1, Ar.sub.2, Ar.sub.3 and Ar.sub.4 may be
carbocyclic or heterocyclic aromatics. Preferably Ar.sub.1,
Ar.sub.2, Ar.sub.3 and Ar.sub.4 are independently benzene or
thiophene.
[0031] Preferably, a plurality of substituents X is provided. It is
preferred that at least one non-terminal ring (Ar.sub.1 or
Ar.sub.2) is substituted. In one preferred embodiment, at least two
substituents X are provided on the same aromatic ring, preferably
Ar.sub.1.
[0032] The strategically positioned substituent groups X described
above provide enhanced solubility, allowing the compound to be
solution processed. Moreover, these substituent groups allow the
mesogenic region of the compound to self-align into regioregular
structures of close-packed lamellar sheets.
[0033] Preferred substituent groups for solubilisation are alkyl
groups, preferably C.sub.4--C.sub.18 alkyl, most preferably octy,
decyl and hexydecyl.
[0034] Meanwhile, the large, rigid coplanar structures provided by
compounds of the invention give extended pi-conjugation and
increased inter- and intra-molecular mobility.
[0035] Preferably, some or all of Ar.sub.2 to Ar.sub.4 comprise
heterocyclic aromatic groups.
[0036] The compound of formula (I) may be fused to one or more
further aryl groups. Thus, in one preferred embodiment, a further
aryl group Ar.sub.5 is fused with Ar.sub.3 to provide a
structure:
##STR00003##
[0037] The further aryl group Ar.sup.5 may comprise a heterocyclic
aromatic group. In this case, substituents X are preferably
provided at least on one or more of the non-terminal aryl groups
Ar.sub.1, Ar.sub.2 and Ar.sub.3.
[0038] Each of Ar.sub.4 and Ar.sub.5 is optionally substituted.
[0039] In certain embodiments, Ar.sub.4 may be fused to a further
aryl system Ar.sub.6 to provide a structure:
##STR00004##
[0040] which aryl system Ar.sub.6 is optionally substituted and may
comprise a heterocyclic aromatic group.
[0041] In this case, substituents X are preferably provided on one
or more of the non-terminal aryl groups Ar.sub.1, Ar.sub.2,
Ar.sub.3 and Ar.sub.4.
[0042] In some embodiments, Ar.sub.5 is fused to a further aryl
system Ar.sub.7 to provide a structure:
##STR00005##
[0043] where the aryl system Ar.sub.7 is optionally substituted and
may comprise a heterocyclic aromatic group.
[0044] In this case, substituents X are preferably provided on one
or more of the non-terminal aryl groups Ar.sub.1, Ar.sub.2,
Ar.sub.3, Ar.sub.4 and Ar.sub.5.
[0045] The above structures illustrate compounds having from 4 to 7
fused rings, however it will be appreciated that yet further rings
may be fused to these compounds to form compounds having
conjugation extending across 8 or more fused rings.
[0046] Preferably, structure II comprises:
##STR00006##
[0047] where Z.sub.1 and Z.sub.2 are independently S, O, Se or NR;
W.sub.1 and W.sub.2 are independently S, O, Se, NR or
--CR.dbd.CR--; R is H or a substituent group; and X.sub.1 and
X.sub.2, which may be the same or different, are selected from
substituents X.
[0048] Preferably, the structure IV comprises the structure:
##STR00007##
[0049] where V.sub.1 and V.sub.2 are independently S, O, Se, NR, NR
or --CR.dbd.CR--.
[0050] More preferably, the structure IV comprises the
structure:
##STR00008##
[0051] Preferably, one or both of the terminal aryl groups of
structures Ito IV is substituted with one or more substituent
groups X one of which groups comprises a reactive or polymerisable
group or optionally substituted straight, branched or cyclic alkyl
chains having 1 to 20 carbon atoms, alkoxy, amino, amido, silyl,
alkyl or alkenyl, the remaining groups independently comprising
hydrogen or optionally substituted straight, branched or cyclic
alkyl chains having 1 to 20 carbon atoms, alkoxy, amino, amido,
silyl, alkyl or alkenyl.
[0052] The reactive or polymerisable groups preferably
independently comprise such moieties as halogens; boronic acids,
diboronic acids and esters of boronic acids and diboronic acids;
alkylene groups; and stannyl groups.
[0053] The terminal aryl groups represent aryl groups fused to just
one other aryl group, for example, structure III has terminal aryl
groups Ar.sub.4 and Ar.sub.3, while structure IV has terminal aryl
groups Ar.sub.6 and Ar.sub.7. For instance, structure IV may
comprise the structure:
##STR00009##
[0054] wherein X.sub.1--X.sub.10, which may be the same or
different, are selected from substituents X described above.
[0055] In some embodiments, the compound comprises a small molecule
comprising any of structures I to IV. In other embodiments, the
compound may comprise an oligomer or a polymer having a repeat unit
comprising any of structures I to IV.
[0056] In one embodiment, the organic semiconducting device is a
thin film transistor.
[0057] In a second aspect, the invention relates to an optical
device comprising a thin film transistor as described herein. In
one embodiment of the second aspect the optical device is an
organic electroluminescent device. In another embodiment the
optical device is a photo responsive device such as a photovoltaic
device or a photo sensor.
[0058] In a third aspect, the invention provides an organic
semiconducting compound comprising one or more of the structures I
to IV.
[0059] In a further aspect, the present invention relates to a
solution for forming a thin film transistor, the solution having a
solute comprising a compound comprising one or more of structures I
to IV and a solvent. Preferably, the solvent is selected from the
group comprising substituted benzenes, preferably benzene
substituted with one or more substituents selected from halogen and
alkyl, for example tetralin, n-butylbenzene, toluene, chlorobenzene
and 1,3,5-trimethylbenzene.
[0060] Preferably, the concentration of the compound of formula (I)
is more than 0.5% weight per volume, preferably 1.0% w/v and most
preferably 2.0% w/v. This concentration may be achieved by the
provision of solubilising groups X.
[0061] In a further aspect, the invention relates to a method for
forming a transistor comprising applying a solution having a solute
comprising a compound comprising any of structures I to IV onto a
substrate. Preferably, the solution is applied by ink-jet
printing.
[0062] In a further aspect, the invention relates to a method for
synthesising a semiconductive compound, the method comprising
fusing one or more further aryl groups to a compound comprising the
structure:
##STR00010##
[0063] where Z.sub.1 and Z.sub.2 are independently S, O, Se or NR ,
where R is H or a substituent group, and X.sub.1 and X.sub.2
independently comprise one of (i) optionally substituted straight,
branched or cyclic alkyl chains with 1 to 20 carbon atoms, alkoxy,
amino, amido, silyl or alkenyl, wherein 2 or more substituents X
may be linked to form a ring or (ii) a polymerisable or reactive
group selected from the group consisting of halogens, boronic
acids, diboronic acids and esters of boronic acids and diboronic
acids, alkylene groups and stannyl groups.; and wherein the one or
more of the further aryl groups may be heterocyclic.
[0064] Preferably, structures I-IV are synthesized by means of a
Suzuki reaction--this is desirable because it avoids the problems
of metallic catalyst residues and delicate reaction conditions
associated with other methods--followed by an acid induced
intramolecular cyclization reaction.
[0065] Exemplary compounds according to the present invention
include the following:
##STR00011##
[0066] wherein X.sub.11--X.sub.13, which may be the same or
different, are selected from substituents X described above.
[0067] Polymerisation of these compounds, if desired, may be
performed using techniques such as Suzuki, Stillie or Yamamoto
polymerization. Exemplary polymers formed by such polymerization
are as follows:
##STR00012##
BRIEF DESCRIPTION OF THE FIGURES
[0068] Embodiments of the invention will now be described, by way
of example only, and with reference to the accompanying drawings in
which:
[0069] FIG. 1 shows a synthesis of a compound according to the
invention, as also described in Intermediates 1 to 4 and Example
1.
[0070] FIG. 2 shows performance data for an organic field effect
transistor device of Example 3, which includes the semiconductor
synthesised in Example 1.
[0071] FIG. 3 shows performance data for an organic field effect
transistor device of Example 3, which includes the semiconductor
synthesised in Example 1.
[0072] FIG. 4 is a schematic diagram of a general architecture of a
bottom-gate organic thin film transistor according to the prior
art;
[0073] FIG. 5 is a schematic diagram of a pixel comprising an
organic thin film transistor and an adjacent organic light emitting
device fabricated on a common substrate according to an embodiment
of the present invention; and,
[0074] FIG. 6 is a schematic diagram of an organic thin film
transistor fabricated in a stacked relationship to an organic light
emitting device according to an embodiment of the present
invention.
DETAILED DESCRIPTION
[0075] Throughout the following description like reference numerals
shall be used to identify like parts.
[0076] Organic semiconductors according to the present invention
may be manufactured by means of a Suzuki coupling reaction followed
by an acid induced intramolecular cyclization reaction as described
below [FIG. 1].
Intermediate 1
##STR00013##
[0078] A solution of 3-bromothiophene (100 g, 0.61 mol) in diethyl
ether (750 ml) under nitrogen was cooled to -78.degree. C. and
n-butyllithium (294.4 ml, 0.74 mmol, 2.5M in hexanes) added drop
wise. After stirring for a further 20 minutes at this temperature,
the mixture was transferred via cannula to an ice cool solution of
methyldisulfide (144.3 g, 1.53 mmol) in diethyl ether (550 ml); the
reaction mixture was warmed to room temperature and stirred at this
temperature for a further 12 hrs. Water (500 ml) was added and the
organic layer separated, washed with water, dried (MgSO.sub.4) and
concentrated under reduced pressure. Distillation of the crude
product gave Intermediate 1 as a yellow oil (43.1 g, 54%,
70.degree. C., 15 mmHg).
Intermediate 2
##STR00014##
[0080] To a stirred solution of Intermediate 1 (42 g, 0.32 mol) in
acetic acid (200 ml) at 15.degree. C., was added N-bromosuccinimide
(57.4 g, 0.32 mol) portion wise at such a rate so as to maintain
the temperature between 15.degree. C. and 17.degree. C. The
resulting mixture was allowed to warm to room temperature
overnight, poured into water and extracted with dichloromethane.
The organic phase was washed with water, saturated aqueous
NaHCO.sub.3, dried (MgSO.sub.4) and concentrated under reduced
pressure. Purification by column chromatography (silica gel,
hexane) gave Intermediate 2 as colourless oil (32 g, 48%).
Intermediate 3
##STR00015##
[0082] To a solution of Intermediate 2 (18 g, 86.1 mmol) in
dichloromethane (360 ml) at 0.degree. C., was added
3-chloro-perbenzoic acid (31.2 g, 90.4 mmol, 50-55%) portion wise
and the resulting solution allowed to stir at room temperature for
12 hrs. The reaction mixture was washed with aqueous
Na.sub.2CO.sub.3, dried (MgSO.sub.4) and concentrated under reduced
pressure to give Intermediate 3 as an yellow oil (15.2 g, 78%).
This was used without any further purification. .sup.1H NMR
(CDCl.sub.3, 400 MHz) .delta..sub.ppm 7.44 (1H, d, J=6.3 Hz), 7.36
(1H, d, J=6.3 Hz), 2.80 (3H, s).
Intermediate 4
##STR00016##
[0084] A solution of Intermediate 3 (11.2 g, 49.75 mmol) and
2,5-dioctylphenylene-1,4-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolate)(12
g, 21.66 mmol) in toluene was degassed with nitrogen for 1 hr.
Pd(PPh.sub.3).sub.4 (1.25 g, 0.05 mol %) was added followed by a
solution of K.sub.2CO.sub.3 (10%, 8.97 g, 64.90 mmol) and a few
drops of Aliquat 336 after a further 5 mins and the mixture allowed
to stir at reflux for 24 hrs. The mixture was diluted with toluene,
the aqueous phase separated, and the organics filtered through
celite, washed with water, dried (MgSO.sub.4) and concentrated
under reduced pressure. Purification by column chromatography
(silca gel, 10% methanol/dichloromethane) gave intermediate 4 as a
beige solid (10.3 g, HPLC 82%) which was used without further
purification. .sup.1H NMR (CDCl.sub.3, 400 MHz) .delta..sub.ppm
7.60 (2H, d, J=5.9 Hz), 7.53 (2H, d, J=5.9 Hz), 7.14 (2H, s), 2.70
(6H, s), 2.52 (4H, m), 1.48 (4H, m), 1.20 (20H, m), 0.85 (6H, t,
J=7.4 Hz).
EXAMPLE 1
##STR00017##
[0086] A solution of Intermediate 4 (1 g, 1.69 mmol) in Eaton's
Reagent (7 ml) was stirred at room temperature in the dark for 48
hrs. The dark green solution was poured into ice-water (100 ml) and
the resulting sticky brown solid dissolved in pyridine (60 ml) and
the solution stirred at reflux for 18 hrs. The mixture was cooled,
poured into dichloromethane (600 ml) and washed thoroughly with 2M
HCl and water, it was then dried (MgSO.sub.4) and concentrated
under reduced pressure. Purification by column chromatography
(silica gel, 5% dichloromethane:hexane) gave Example 1 as a white
solid (240 mg, 35%, HPLC 99.6%); mp (DSC) 126.5.degree. C.; .sup.1H
NMR (CDCl3, 400 MHz) .delta..sub.ppm 7.57 (2H, d, J=4.8 Hz), 7.37
(2H, d, J=4.8 Hz), 3.27 (4H, t, J=8 Hz), 1.85 (4H, m), 1.61 (4H,
m), 1.40 (4H, m), 1.30 (12H, m), 0.88 (6H, t, J=7.4 Hz).
EXAMPLE 2
##STR00018##
[0088] Example 2 was synthesized in a similar manner to that
described for Example 1 by means of a Suzuki coupling reaction
followed by an acid induced intramolecular cyclization
reaction.
EXAMPLE 3
[0089] Organic field effect transistor devices using compound of
Example 1 as the active layer were fabricated in a top gate, bottom
contact device. Gold source drain contacts were defined by lift off
on a glass substrate. Channel lengths of 10-200 .mu.m and widths of
2 mm were defined. Devices were fabricated by spin-coating the
compound of example 1, onto the cleaned substrates from a 2%
tetralin solution at 1000 rpm for 60 seconds. The film was
subsequently dried on a hotplate at 80.degree. C. for 10 mins and
cooled on a metal block for 1 minute. A fluorinated dielectric
material was spin-coated from a fluorosolvent on to the
semiconductor layer, dried on a hotplate at 80.degree. C. for 10
mins and cooled on a metal block for 1 min. The highest mobility in
saturation observed was 0.71 cm.sup.2/Vs at 100 .mu.m channel
length. An on/off ratio of .about.10.sup.4 was obtained. A contact
resistance of 27 kOhm-cm was calculated by the extrapolation method
at -40V Vg or a gate field of 16V/100 nm [FIG. 2].
EXAMPLE 4
[0090] Organic field effect transistor devices using compound of
Example 2 as the active layer were fabricated in a top gate, bottom
contact device. Gold source drain contacts were defined by lift off
on a glass substrate. Channel lengths of 10-200 .mu.m and widths of
2 mm were defined. Devices were fabricated by spin-coating the
compound of example 2, onto the cleaned substrates, from a 2%
1,3,5-trimethylbenzene solution at 1000 rpm for 60 secs, the
semiconductor solution, substrate and spin coater chuck were all
raised to elevated temperatures (80.degree. C.) immediately prior
to the spin coating step of the material. The film was subsequently
dried on a hotplate at 80.degree. C. for 5 mins and cooled on a
metal block for 1 min. A fluorinated dielectric material was
spin-coated from a fluorosolvent on to the semiconductor layer,
dried on a hotplate at 80.degree. C. for 10 mins and cooled on a
metal block for 1 min. The highest mobility in saturation observed
was 0.05 cm.sup.2/Vs at 50 .mu.m channel length. An on/off ratio of
10.sup.-5 was obtained. A contact resistance of 180 kOhm-cm was
calculated by the extrapolation method at -40V Vg or a gate field
of 16V/100 nm [FIG. 3].
[0091] The resulting compounds are easily soluble and may thus be
applied by ink-jet printing onto a substrate to provide the
semiconducting layer 15 in a thin film transistor such as is shown
in FIG. 4.
[0092] An application of such an organic thin film transistor
(OTFT) may be to drive pixels in an optical device, preferably an
organic optical device. Examples of such optical devices include
photoresponsive devices, in particular photodetectors, and
light-emissive devices, in particular organic light emitting
devices. OTFTs are particularly suited for use with active matrix
organic light emitting devices, e.g. for use in display
applications.
[0093] FIG. 5 shows a pixel comprising an organic thin film
transistor 100 and an adjacent organic light emitting device (OLED)
102 fabricated on a common substrate 104. The OTFT 100 comprises
gate electrode 106, dielectric layer 108, source and drain
electrodes 110 and 112 respectively, and OSC layer 114. The OLED
102 comprises anode 116, cathode 118 and an electroluminescent
layer 120 provided between the anode 116 and cathode 118. Further
layers may be located between the anode 116 and cathode 118, such
as charge transporting, charge injecting or charge blocking layers.
In the embodiment of FIG. 5, the layer of cathode material 118
extends across both the OTFT 100 and the OLED 102, and an
insulating layer 122 is provided to electrically isolate the
cathode layer 118 from the OSC layer 114. The active areas of the
OTFT 100 and the OLED 102 are defined by a common bank material
formed by depositing a layer of photoresist 124 on substrate 104
and patterning it to define OTFT 100 and OLED 102 areas on the
substrate.
[0094] In FIG. 5, the drain electrode 112 is directly connected to
the anode 116 of the organic light emitting device 102 for
switching the organic light emitting device 102 between emitting
and non-emitting states.
[0095] In an alternative arrangement illustrated in FIG. 6, an
organic thin film transistor 200 may be fabricated in a stacked
relationship to an organic light emitting device 202. In such an
embodiment, the organic thin film transistor 202 is built up as
described above in either a top or bottom gate configuration. As
with the embodiment of FIG. 5, the active areas of the OTFT 200 and
OLED 202 are defined by a patterned layer of photoresist 124,
however in this stacked arrangement, there are two separate bank
layers 124--one for the OLED 202 and one for the OTFT 200. A
planarisation layer 204 (also acting as a passivation layer) is
deposited over the OTFT 200. Exemplary passivation layers 204
include BCBs and parylenes. The organic light emitting device 202
is fabricated over the passivation layer 204 and the anode 116 of
the organic light emitting device 202 is electrically connected to
the drain electrode 112 of the OTFT 200 by a conductive via 206
passing through passivation layer 204 and bank layer 124.
[0096] It will be appreciated that pixel circuits comprising an
OTFT and an optically active area (e.g. light emitting or light
sensing area) may comprise further elements. In particular, the
OLED pixel circuits of FIGS. 5 and 6 will typically comprise least
one further transistor in addition to the driving transistor shown,
and at least one capacitor. It will be appreciated that the organic
light emitting devices described herein may be top or
bottom-emitting devices. That is, the devices may emit light
through either the anode or cathode side of the device. In a
transparent device, both the anode and cathode are transparent. It
will be appreciated that a transparent cathode device need not have
a transparent anode (unless, of course, a fully transparent device
is desired), and so the transparent anode used for bottom-emitting
devices may be replaced or supplemented with a layer of reflective
material such as a layer of aluminium.
[0097] Transparent cathodes are particularly advantageous for
active matrix devices because emission through a transparent anode
in such devices may be at least partially blocked by OTFT drive
circuitry located underneath the emissive pixels as can be seen
from the embodiment illustrated in FIG. 6.
[0098] Thicknesses of the gate electrode, source and drain
electrodes may be in the region of 5-200 nm, although typically 50
nm as measured by Atomic Force Microscopy (AFM), for example.
[0099] Other layers may be included in the device architecture. For
example, in addition to providing a self assembled monolayer (SAM)
on the gate, source or drain electrodes one may be provided on the,
substrate, insulating layer and organic semiconductor material to
promote crystallinity, reduce contact resistance, repair surface
characteristics and promote adhesion where required. In particular,
the dielectric surface in the channel region may be provided with a
monolayer comprising a binding region and an organic region to
improve device performance, e.g. by improving the organic
semiconductor's morphology (in particular polymer alignment and
crystallinity) and covering charge traps, in particular for a high
k dielectric surface. Exemplary materials for such a monolayer
include chloro- or alkoxy-silanes with long alkyl chains, e.g.
octadecyltrichlorosilane.
[0100] No doubt many other effective alternatives will occur to the
skilled person. It will be understood that the invention is not
limited to the described embodiments and encompasses modifications
apparent to those skilled in the art lying within the scope of the
following claims.
* * * * *